A fertile convergence of anatomical, electrophysiological, psychophysical, functional imaging and computational approaches has made visual motion one of the most active areas of research with a number of important well-defined problems that are yielding to rigorous investigation. We expect that the outcome of the research program proposed here will contribute in important ways to our understanding of the functional architecture of the human visual motion system by a) elucidating the nature and organization of the mechanisms involved in the visual guidance of navigation, and b) investigating whether a particular anatomical region is computationally necessary for specific visual functions. The method by which we will address this is through studying the performance of neurological patients with discrete lesions on talks specifically designed to address the cortical mechanisms believed to underlie visual navigation. How does locomotor guidance depend on optic flow, 3D scene structure, and the recognition of landmarks? Are motion and stereo integrated at different stages in this process? We have previously developed a psychophysical paradigm of computer generated motion stimuli designed to critically analyze motion. Within this paradigm we shall now develop a new set of tasks designed to examine the effect of discrete brain lesions in neurological patients on (1) the perception of speed and direction of complex motion patterns, discrimination of the center of motion, heading perception; (2) the interaction between stereopsis and global motion and how different cues for 3D perception are processed; (3) perceptual-motor actions. Progress in understanding the neural substrate and the mechanisms underlying specific deficits in motion for navigation will provide important clues for how perception is linked to action. The correlation of neuroimaging, neuro-ophthalmological, neurological and neuropsychological examinations with patients' performance on the psychophysical tasks of visual navigation described in this proposal will be useful for devising diagnostic and mediation strategies.